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    <meta charset="UTF-8">
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    <title>Document</title>
</head>

<body>
    <button id="ldh">刘德华</button>
    <button id="zxy">张学友</button> <br>
    <img src="images/ldh.jpg" alt="" title="刘德华">
</body>
<script>
    var ldh = document.getElementById('ldh');
    var zxy = document.getElementById('zxy');
    var img = document.querySelector('img');
    ldh.onclick = function () {
        img.src = "images/ldh.jpg";
        img.title = "刘德华";
    }
    zxy.onclick = function () {
        img.src = "images/zxy.jpg";
        img.title = "张学友";
    }
</script>

</html>